This invention relates to a multi-cylinder engine and more particularly to an improved management system and control method for such engines.
In many forms of internal combustion engines, there are times when the engine is operated with less than its total number of cylinders running. That is, during the operation of the engine, one or more cylinders may be intentionally disabled and prevented from undergoing combustion. This is done for a variety of purposes.
For example, it has been the practice at times to limit the maximum power output of an engine and to improve its efficiency under some running conditions by disabling certain cylinders. The disabled cylinder or cylinders are prevented from undergoing combustion either by intentionally not firing or misfiring the spark plugs and/or by selectively disabling the supply of fuel to those cylinders. This permits the engine to operate as a variable displacement engine. Thus only the displacement necessary for any given running condition is employed. This permits increases in the overall efficiency.
This same technique is utilized with engines to permit them to continue to propel the vehicle, but under a reduced speed in the event of some malfunction in the engine. These so called "limp home" modes of operation protect the engine from serious damage, but nevertheless permit the occupants to reach a location where assistance can be obtained.
Another use for such cylinder disabling is disclosed in the copending application of Kazuhiro Nakamura and Kimihiro Nonaka entitled "Combustion Control System for Internal Combustion Engine," Ser. No. 08/299,517, filed Sep. 1, 1994 and assigned to the assignee hereof. In that application, the engine is operated so that the throttle valve is positioned in a substantial partially opened condition under idle and off idle conditions. This improves the performance of the engine on acceleration.
That is, the throttle valve is held more fully opened than with conventional engines so that the engine could induct more air than is necessary for its operation at the idle or off idle speed. The actual engine speed is controlled to the desired speed by selectively disabling one or more cylinders of the engine. The actual number of cylinders disabled will be determined by the actual desired speed for the engine. This system significantly improves engine performance.
With such systems, obviously the number of running or operating cylinders will change, particularly during transient conditions. It is extremely important to see that the transitional phase can be accomplished smoothly so that the full advantages of this concept can be enjoyed.
Specifically, if the engine has been operating at a reduced speed by operating with less than all cylinders or combustion chambers firing and cylinders are added, there can be a sudden and abrupt increase in the speed of the engine. In a like manner, if the engine is operating at a certain speed and it is desired to reduce that speed, the discontinued firing of a cylinder or additional cylinders or combustion chambers can cause the speed to reduce rather abruptly. Aside from being disconcerting to the operator, these sudden changes in speed can add to the wear on the various components of this system.
It is, therefore, a principal object of this invention to provide an improved engine speed control arrangement wherein the speed is controlled by varying the number of operating combustion chambers and wherein transition from more to less operating combustion chambers is done more smoothly.
It should be noted that, although reference is made to "cylinders" the same principles may be applied to rotary engines. Hence the terms "cylinders" or "combustion chambers" as used herein are intended to encompass either reciprocating or rotary engines, unless otherwise so specified.